The present invention relates generally to sensors responsive to a predetermined level of acceleration or deceleration. The sensor may be used in a supplemental passenger restraint system comprising an inflatable bag and gas generator which is activated upon receipt of the signal.
As mentioned above, the present invention is generally related to acceleration or deceleration sensors. These sensors may be referred to as velocity change sensors, inertia switches, acceleration or deceleration sensors, or crash sensors. Commonly used in the above class of sensors is an inertial mass or slug which moves from a first position to a second position to complete a circuit across a plurality of electrical contacts in response to a predetermined acceleration pulse. In the following text, acceleration or deceleration are used interchangeably. Various means have been used to maintain the inertial mass in the first position below acceleration pulses of a predetermined magnitude. U.S. Pat. No. 4,329,549 and U.S. Pat. No. 3,774,126 magnetically bias the inertial mass toward the first position. In contrast, U.S. Pat. No. 4,097,699 a spring biases an inertial mass towards the first position. U.S. Pat. No. 4,329,549 and 4,097,699 incorporate a mechanism for damping the inertial mass to insure that it will not be actuated unless the acceleration pulse (amplitude and time) exceeds a certain level for a predetermined period of time. Both of these patents use an extremely small diametral clearance between the inertial mass and a tube such that as the inertial mass is moved from the first position toward the second position, gas within the tube generates a damping force impeding the motion of the inertial mass. A shortcoming of this type of sensor is that the clearances between the tube and the inertial mass must be controlled exactly in order to generate the necessary viscous damping force. Such exact tolerances inevitably complicate production and increase the cost of the device. In addition, these devices require exotic sealing mechanisms to prevent moisture from entering the tube since if fluid or vapor enters the tube the viscous damping characteristics will change causing the device to malfunction.
It is an object of the present invention to provide an acceleration responsive sensor which solves the problems associated with the prior art. A further object of the invention is to generate a counter-electromagnetic force operative on an inertial mass to dampen its motion.
Accordingly, the invention comprises: a sensor comprising: an inertial mass movable from a first position to a second position in response to an acceleration signal of predetermined amplitude and duration; first means for indicating that the inertial mass has moved to the second position; second means for generating an electro-magnetic force tending to dampen the motion of the inertial mass; and third means for biasing the inertial mass towards the first position.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.